pm: cpupower: Clean up bindings gitignore

Add SPDX identifier to the gitignore. Remove the comment and .i file
since the file it references was removed in another patch. This patch
depends on Min-Hua Chen's 'pm: cpupower: rename raw_pylibcpupower.i'.

Signed-off-by: John B. Wyatt IV <jwyatt@redhat.com>
Signed-off-by: John B. Wyatt IV <sageofredondo@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>